1. Field of the Invention
This invention relates to a camera having a type of zoom lens in which a lens barrel can be collapsed in a camera body.
2. Description of the Related Art
Non-lens-interchangable type compact cameras having a zoom lens mechanism have recently been placed on the market. For example, a camera of this type, such as that shown in FIG. 11, is known.
In the camera shown in FIG. 11, the positions of fore and rear groups of a photographing optical system are controlled with one cam ring 201 and a straight-drive cam 202 to position the two lens groups at focal distances which change continuously. A gear 201a is formed on a rear outer-circumferential portion of the cam ring 201. The gear 201a is driven with a gear 203 to which a driving force is transmitted from a power source to perform zooming.
In the arrangement shown in FIG. 11, the whole lens barrel including the cam ring 201 and the straight-drive cam 202 can be collapsed in the body by an operation using a retraction cam ring 205 and a retraction straight-drive cam 204 slidably engaging with a pin 204' embedded in the straight-drive cam 202.
The conventional zooming mechanism shown in FIG. 11 entails the following problems.
(a) To prevent the outer circumferential gear portion 201a provided on the cam ring 201 from interfering with an inner circumferential portion of the straight-drive cam 204 when the lens barrel is collapsed, it is necessary to increase the diameters of the cam 204 and the cam ring 205. However, the overall size of the camera is increased if the cam 204 and the cam ring 205 are increased.
(b) To maintain the engagement between the gear 203 and the gear 201a while the lens barrel is retracted, it is necessary to extend the gear portion 201a of the cam ring 201 as indicated at 201b. However, if such an extended gear portion 201b is provided, it must be covered with an outer casing portion of the camera so that it is not exposed outside the camera even when put out from the collapsed position, resulting in an increase in the outside diameter of the lens barrel cover.
(c) If the cam ring 201 is exposed outside when the lens barrel is put out from the collapsed position, the cam ring 201 having the rotating cam groove can be seen from the outside so that the appearance of the camera is marred and, moreover, there is a risk of a light leak through the cam groove. To prevent this risk, it is necessary to form an outer casing 206 so as to cover the cam ring 201 and the straight-drive cam 202. This design has a contrary effect; the thickness of the camera is increased in comparison with conventional cameras, although the lens barrel unit can be collapsed in the camera body.
The applicant of the present invention has proposed a camera disclosed in Japanese Patent Application No. 1-320130 (now, Japanese Laid-Open Patent No. 3-180826) to solve this problem.
The zoom lens barrel of this camera is generally constituted of three lens groups. The positions of the first and second lens groups are controlled by the rotation of a cam ring, and the third lens group is driven by another driving mechanism. These three lens groups are operated for zooming, and the third lens group is used as a focusing lens. An input gear formed of a gear train meshing with an internal teeth formed on an inner circumferential surface of a rear end portion of the cam ring and an output gear of the zoom driving mechanism provided on the camera body are connected at a lens barrel put-out position to transmit a zoom driving force to the cam ring.
However, the input gear and the output gear constituting the zoom driving mechanism are disconnected when the lens barrel is retracted into the camera body, and there is a possibility of these gears rotating relative to each other to be out of phase when the camera is carried so that the gears cannot be connected smoothly when the lens is put out for photographing.
There is also a problem that a diverging torque from the output gear cannot be used to drive a zoom finder. This is because if the input and output gears become out of phase, the phase of a cam for making a torque diverge from the output gear to drive a lens of the finder by a well-known means is shifted.